As a technique for measuring a molecular vibration spectrum of a sample, Fourier-transform spectroscopy is known, such as Fourier-transform infrared spectroscopy (also referred to as FT-IR) (cf. Patent Literature 1) and Fourier-transform coherent anti-Stokes Raman scattering (also referred to as FT-CARS) spectroscopy (cf. Non Patent Literature 1).
In the Fourier-transform spectroscopy, an interference wave is produced using a Michelson interferometer in which light emitted from a light source is split by a beam splitter into reference light which propagates in a first arm including a fixed mirror and scanning light which propagates in a second arm including a movable mirror, and the reference light reflected on the fixed mirror of the first arm is combined with the scanning light reflected on the movable mirror of the second arm, and the sample is then irradiated with the produced interference wave.
In the Fourier-transform spectroscopy, in the Michelson interferometer, the movable mirror is moved in one direction to change a light path length of the second arm and delay the scanning light with respect to the reference light, thereby producing an interferogram of an interference wave, and a Fourier transform of the interferogram is performed to obtain a molecular vibration spectrum.
In the FT-IR, an interferogram of transmitted light, generated by transmission of an interference wave through a sample, is produced and a Fourier transform of the interferogram is performed, to obtain a molecular vibration spectrum of the sample.
In the FT-CARS spectroscopy, an interferogram of anti-Stokes light, emitted due to coherent anti-Stokes Raman scattering which has occurred in a sample by irradiation with an interference wave, is produced and a Fourier transform of the interferogram is performed to obtain a molecular vibration spectrum of the sample.
As thus described, in the Fourier-transform spectroscopy, an interferogram is produced by delaying the scanning light with respect to the reference light by using the Michelson interferometer, and a Fourier transform of the interferogram is performed to obtain a molecular vibration spectrum.